Compressor

ABSTRACT

A stator core of a motor has a plurality of oil return passages extending through one surface and the other surface of the core. On the other surface of the stator core, a hydraulic diameter of each oil return passage is 5 mm or larger, and a ratio of a total area of the oil return passages to an area of a virtual circle having a diameter equal to a maximum outer diameter of the stator core is 5 to 15%. Lubricating oil accumulated on the other surface side of the stator core is returned to an oil reservoir through the oil return passages, and shortage of oil in the oil reservoir is prevented. Furthermore, a cross sectional area of the stator core can be securely kept, and motor efficiency is maintained.

TECHNICAL FIELD

The present invention relates to a compressor to be used for, forexample, air conditioners, refrigerators and the like.

BACKGROUND ART

Conventionally, a compressor includes a closed container, a compressionelement placed within the closed container, and a motor placed in theclosed container and acting to drive the compression element via ashaft, with an oil reservoir formed at a bottom portion of the closedcontainer so that lubricating oil is accumulated in the oil reservoir(see JP 2003-262192 A).

However, in the conventional compressor described above, becausepassages extending through from upper to lower portions of the motor aresmall, lubricating oil accumulated in the upper portion of the motorless returns to the oil reservoir located lower than the motor. Thiswould cause occurrence of shortage of oil in the oil reservoir, as aproblem. As a result of this shortage of oil, it would be impossible toeffectively feed the lubricating oil in the oil reservoir via the shaftto sliding parts such as the compression element or the bearing of themotor, resulting in deteriorated reliability of the compressor. Inparticular, when carbon dioxide is used as the refrigerant, involvinguse of a high-viscosity lubricating oil as the lubricating oil, thelubricating oil would be even less return to the oil reservoir.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide acompressor which is prevented from shortage of oil in the oil reservoirwhile motor efficiency of a motor is maintained.

In order to achieve the above object, the present invention provides acompressor comprising:

a closed container having an oil reservoir;

a compression element placed within the closed container; and

a motor which is placed within the closed container and which drives thecompression element via a shaft, wherein

a stator core of the motor has a plurality of oil return passagesextending through one surface of the stator core located on its one sidecloser to the oil reservoir and the other surface of the stator corelocated on its another side opposite to the oil reservoir, and

on the other surface of the stator core,

a hydraulic diameter of each of the oil return passages is 5 mm orlarger, and a ratio of a total area of the plurality of oil returnpassages to an area of a virtual circle having a diameter equal to amaximum outer diameter of the stator core is 5 to 15%.

In the compressor of the present invention, in the other surface of thestator core, the hydraulic diameter of each of the oil return passagesis 5 mm or larger, and the ratio of the total area of the plurality ofoil return passages to the area of the virtual circle having thediameter equal to the maximum outer diameter of the stator core is 5 to15%. Therefore, lubricating oil accumulated on the other surface side ofthe stator core can be returned to the oil reservoir located on the onesurface side of the stator core via the plurality of oil returnpassages, so that oil shortage in the oil reservoir can be prevented.Moreover, the cross-sectional area of the stator core can be ensured,and the motor efficiency can be maintained. Particularly when carbondioxide is used as the refrigerant, in which use of a high-viscositylubricating oil is involved, the lubricating oil can effectively bereturned to the oil reservoir.

In one embodiment, the stator core is placed radially outside of a rotorof the motor, and

the oil return passages are located on an outer circumferential side ofthe stator core.

In the compressor of this embodiment, since the oil return passages arelocated on the outer circumferential side of the stator core,lubricating oil that has been scattered radially outward by the rotor orlubricating oil that has stuck to the inner circumferential surface ofthe closed container can effectively be led to the oil return passages,so that oil shortage in the oil reservoir can be prevented morereliably.

In one embodiment, a refrigerant in the closed container is carbondioxide.

In the compressor of this embodiment, since the refrigerant within theclosed container is carbon dioxide, in which use of a high-viscositylubricating oil is involved, the lubricating oil can effectively bereturned to the oil reservoir.

According to the compressor of the present invention, in the othersurface of the stator core, the hydraulic diameter of each of the oilreturn passages is 5 mm or larger, and the ratio of the total area ofthe plurality of oil return passages to the area of the virtual circlehaving the diameter equal to the maximum outer diameter of the statorcore is 5 to 15% so that oil shortage in the oil reservoir can beprevented and the motor efficiency can be maintained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view showing an embodiment of acompressor of the invention;

FIG. 2 is a plan view of main part of the compressor;

FIG. 3 is a cross-sectional view of a vicinity of a motor in thecompressor;

FIG. 4 is an enlarged view of part A of FIG. 3;

FIG. 5 is a graph showing relationships of oil shortage and motorefficiency with hydraulic diameter and area ratio;

FIG. 6A is a graph showing a relationship between area ratio andmotor-efficiency decreasing rate;

FIG. 6B is a graph showing a relationship between area ratio andoil-level decreasing rate;

FIG. 7A is a graph showing a relationship between hydraulic diameter andmotor-efficiency decreasing rate;

FIG. 7B is a graph showing a relationship between hydraulic diameter andoil-level decreasing rate.

DETAILED DESCRIPTION OF THE INVENTION

Hereinbelow, the present invention will be described in detail by way ofembodiments thereof illustrated in the accompanying drawings.

FIG. 1 shows a longitudinal sectional view which is an embodiment of acompressor of the invention. This compressor includes a closed container1, a compression element 2 placed within the closed container 1, and amotor 3 placed in the closed container 1 and acting to drive thecompression element 2 via a shaft 12.

This compressor is a so-called vertical high-pressure dome-type rotarycompressor, in which the compression element 2 is placed below and themotor 3 is placed above within the closed container 1. The compressionelement 2 is driven by a rotor 6 of the motor 3 via the shaft 12.

The compression element 2 sucks in a refrigerant gas from an accumulator10 through a suction pipe 11. The refrigerant gas can be obtained bycontrolling unshown condenser, expansion mechanism and evaporator thatconstitute an air conditioner as an example of a refrigeration system incombination with the compressor.

The refrigerant gas, which is carbon dioxide, becomes as high a pressureas about 12 MPa within the closed container 1. Alternatively, R410A orR22 or other like refrigerant may be used as the refrigerant.

In this compressor, a compressed high-temperature, high-pressurerefrigerant gas is discharged from the compression element 2 to fill theclosed container 1 therewith internally, while the refrigerant gas ispassed through a gap between the stator 5 and the rotor 6 of the motor 3to cool the motor 3. The refrigerant gas is thereafter dischargedoutside from a discharge pipe 13 provided on the upper side of the motor3.

In lower portion of a high-pressure region within the closed container 1is formed an oil reservoir 9 in which lubricating oil is accumulated.This lubricating oil moves from the oil reservoir 9 through oil passages(not shown) provided in the shaft 12 to sliding parts such as thecompression element 2 and a bearing of the motor 3, thus lubricating thesliding parts.

When carbon dioxide is used as the refrigerant, the lubricating oil tobe used is a high-viscosity one. As this lubricating oil, a lubricatingoil having a viscosity of 5-300 cSt at 40° C. is used. This lubricatingoil is exemplified by polyalkylene glycol oil (such as polyethyleneglycol and polypropylene glycol), ether oil, ester oil, and mineral oil.

The compression element 2 includes a cylinder 21 fitted to an innersurface of the closed container 1, and an upper-side end plate member 50and a lower-side end plate member 60 fitted to upper and lower openingends of the cylinder 21, respectively. A cylinder chamber 22 is definedby the cylinder 21, the upper-side end plate member 50 and thelower-side end plate member 60.

The upper-side end plate member 50 has a disc-shaped body portion 51,and a boss portion 52 provided upwardly at a center of the body portion51. The shaft 12 is inserted into the body portion 51 and the bossportion 52. In the body portion 51 is provided a discharge hole 51 acommunicating with the cylinder chamber 22.

A discharge valve 31 is fitted to the body portion 51 so as to bepositioned on one side of the body portion 51 opposite to the side onwhich the cylinder 21 is provided. This discharge valve 31 is, forexample, a reed valve which opens and closes the discharge hole 51 a.

A cup-type muffler cover 40 is fitted on the body portion 51 on its oneside opposite to the cylinder 21 so as to cover the discharge valve 31.The muffler cover 40 is fixed to the body portion 51 by fixing members35 (e.g., bolt). The boss portion 52 is inserted into the muffler cover40.

The muffler cover 40 and the upper-side end plate member 50 define amuffler chamber 42. The muffler chamber 42 and the cylinder chamber 22are communicated with each other via the discharge hole 51 a.

The muffler cover 40 has a hole portion 43. By the hole portion 43, themuffler chamber 42 and an outer side of the muffler cover 40 arecommunicated with each other.

The lower-side end plate member 60 has a disc-shaped body portion 61,and a boss portion 62 provided downwardly at a center of the bodyportion 61. The shaft 12 is inserted into the body portion 61 and theboss portion 62.

In short, one end portion of the shaft 12 is supported by the upper-sideend plate member 50 and the lower-side end plate member 60. That is, theshaft 12 cantilevers. One end portion (on the support end side) of theshaft 12 intrudes into the cylinder chamber 22.

On the support end side of the shaft 12, an eccentric pin 26 is providedso as to be positioned within the cylinder chamber 22 of the compressionelement 2. The eccentric pin 26 is fitted into a roller 27. The roller27 is placed revolvable in the cylinder chamber 22 so that compressionaction is exerted by revolving motion of the roller 27.

In other words, one end portion of the shaft 12 is supported by ahousing 7 of the compression element 2 on both sides of the eccentricpin 26. The housing 7 includes the upper-side end plate member 50 andthe lower-side end plate member 60.

Next, compression action of the cylinder chamber 22 is explained.

As shown in FIG. 2, the cylinder chamber 22 is internally partitioned bya blade 28 integrally provided with the roller 27. That is, in a chamberon the right side of the blade 28, the suction pipe 11 is opened in theinner surface of the cylinder chamber 22 to form a suction chamber(low-pressure chamber) 22 a. In a chamber on the left side of the blade28, the discharge hole 51 a (shown in FIG. 1) is opened in the innersurface of the cylinder chamber 22 to form a discharge chamber(high-pressure chamber) 22 b.

Semicolumnar-shaped bushes 25, 25 are set in close contact with bothsurfaces of the blade 28 to provide a seal. Lubrication with thelubricating oil is implemented between the blade 28 and the bushes 25,25.

Then, as the eccentric pin 26 eccentrically rotates along with the shaft12, the roller 27 fitted to the eccentric pin 26 revolves while theouter circumferential surface of the roller 27 keeps in contact with theinner circumferential surface of the cylinder chamber 22.

As the roller 27 revolves in the cylinder chamber 22, the blade 28 movesback and forth while both side faces of the blade 28 are held by thebushes 25, 25. Then, the low-pressure refrigerant gas is sucked from thesuction pipe 11 into the suction chamber 22 a and compressed into a highpressure in the discharge chamber 22 b, so that a high-pressurerefrigerant gas is discharged from the discharge hole 51 a (shown inFIG. 1).

Thereafter, as shown in FIG. 1, the refrigerant gas discharged from thedischarge hole 51 a is discharged via the muffler chamber 42 outward ofthe muffler cover 40.

As shown in FIGS. 1 and 3, the motor 3 has the rotor 6, and the stator 5placed radially outside of the rotor 6 with an air gap interposedtherebetween.

The rotor 6 has a rotor body 610, and magnets 620 embedded in the rotorbody 610. The rotor body 610 is cylindrical shaped and formed of, forexample, multilayered electromagnetic steel plates. The shaft 12 isfitted to a hole portion at a center of the rotor body 610. Each of themagnets 620 is a flat permanent magnet. Six of the magnets 620 arearrayed at center angles of equal intervals in the circumferentialdirection of the rotor body 610.

The stator 5 has a stator core 510, and coils 520 wound around thestator core 510. In FIG. 3, the coils 520 are partly omitted inillustration.

The stator core 510 has an annular portion 511, and nine teeth 512protruding radially inwardly from an inner circumferential surface ofthe annular portion 511 and arrayed circumferentially at equalintervals. The stator core 510 is formed of a plurality of multilayeredsteel plates. The coils 520 are wound around the individual teeth 512,respectively, and not wound over the plurality of teeth 512, hence aconcentrated winding.

The motor 3 is a so-called 6-pole, 9-slot type one. By electromagneticforce generated in the stator 5 caused by passing a current through thecoils 520, the rotor 6 is rotated along with the shaft 12.

The stator core 510 has a plurality of oil return passages 530 extendingthrough one surface (lower surface) 510 a of the stator core 510 locatedon its one side closer to the oil reservoir 9 and the other surface(upper surface) 510 b of the stator core 510 located on the other sideopposite to the oil reservoir 9.

The oil return passages 530 are located on the outer circumferentialside of the stator core 510. The oil return passages 530 are formed byso-called core cuts of recessed grooves or D-cut surfaces or the likeformed in the outer circumferential surface of the stator core 510. Thatis, the oil return passages 530 are spaces each surrounded by an innersurface of a core cut and an inner circumferential surface 1 b of theclosed container 1.

The oil return passages 530 are provided radially outside of the teeth512, respectively, counting nine equal to that of the teeth 512. The oilreturn passages 530 are formed each into a generally rectangular shapeas viewed along a center axis 1 a of the closed container 1.

In the other surface 510 b of the stator core 510, the hydraulicdiameter of each oil return passage 530 is 5 mm or larger, and the ratioof the total area of the plural oil return passages 530 to the area ofthe virtual circle having a diameter equal to the maximum outer diameterof the stator core 510 (hereinafter, referred to as area ratio) is 5 to15%.

Given an area S of the oil return passage 530 on the other surface 510 band a circumferential length L of the oil return passage 530 on theother surface 510 b as shown in FIG. 4, the hydraulic diameter of theoil return passage 530 can be expressed as 4S/L. FIG. 4 is an enlargedview of part A of FIG. 3.

The area S of the oil return passage 530 is, as shown by hatching inFIG. 4, an area surrounded by the inner surface of the recessed grooveof the stator core 510 and the inner circumferential surface 1 b of theclosed container 1. The circumferential length L of the oil returnpassage 530 is, as shown by bold line in FIG. 4, a value resulting fromadding up a length of the inner surface of the recessed groove of thestator core 510 and a length of the inner circumferential surface 1 b ofthe closed container 1.

The virtual circle having a diameter equal to the maximum outer diameterof the stator core 510 is, as shown in FIG. 3, coincident with the innercircumferential surface 1 b of the closed container 1. That is, the areaof this virtual circle is coincident with a cross-sectional area of theinside of the closed container 1 on the other surface 510 b. The totalarea of the plurality of oil return passages 530 refers to a total sumof areas S of the oil return passages 530 on the other surface 510 b.

According to the compressor constructed as described above, thehydraulic diameter of each oil return passage 530 on the other surface510 b of the stator core 510 is 5 mm or larger, and the area ratio is 5to 15%. Therefore, lubricating oil that has flowed to the downstreamside (upper side) of the motor 3 along with the refrigerant gas so as tobe accumulated on the other surface 510 b side of the stator core 510can be returned to the oil reservoir 9 on the one surface 510 a side ofthe stator core 510 via the plurality of oil return passages 530, sothat oil shortage in the oil reservoir 9 can be prevented. Thus, by thisprevention of oil shortage, lubricating oil in the oil reservoir 9 caneffectively be fed via the shaft 12 to sliding parts such as thecompression element 2 and the bearing of the motor 3, so that thereliability of the compressor is improved.

Moreover, the cross-sectional area of the stator core 510 can beensured, and the motor efficiency can be maintained. Particularly whencarbon dioxide is used as the refrigerant, in which use of ahigh-viscosity lubricating oil is involved, the lubricating oil caneffectively be returned to the oil reservoir 9.

In this case, if the hydraulic diameter of each oil return passage 530satisfies to be 5 mm only on the other surface 510 b of the stator core510, the lubricating oil overcomes the viscosity by its dead weight tomove down along the oil return passages 530 up to the oil reservoir 9.

In contrast to this, if the hydraulic diameter of each oil returnpassage 530 is smaller than 5 mm, then the oil return passages 530 areeach formed into, for example, a slit shape as its planar shape, so thatthe lubricating oil sticks to the other surface 510 b of the stator core510 by its viscosity, thus not going down along the oil return passages530, and not moving to the oil reservoir 9. That is, there is a problemof occurrence of oil shortage. On the other hand, if the hydraulicdiameter of each oil return passage 530 is larger than 15 mm, then theeffective surface area of the annular portion 511 of the stator core 510becomes smaller, resulting in a deteriorated motor efficiency.

Further, if the area ratio is smaller than 5%, then the number of oilreturn passages 530 becomes smaller, so that lubricating oil cannoteffectively be returned to the oil reservoir 9, giving rise tooccurrence of oil shortage as a problem. On the other hand, if the arearatio is larger than 15%, then the number or area of the oil returnpassages 530 becomes larger, causing the surface area of the stator core510 to be smaller, so that the motor efficiency decreases as a problem.

In this invention, preferably, the hydraulic diameter of each oil returnpassage 530 is not more than 20 mm (more preferably, not more than 15mm), in which case the cross-sectional area of the stator core 510 canmore reliably be ensured and the motor efficiency can more reliably bemaintained.

Further, since the oil return passages 530 are located on the outercircumferential side of the stator core 510, lubricating oil that hasbeen scattered radially outward by the rotor 6 or lubricating oil thathas stuck to the inner circumferential surface 1 b of the closedcontainer 1 can effectively be led to the oil return passages 530, sothat oil shortage in the oil reservoir 9 can more reliably be prevented.

Next, FIG. 5 shows relationships of oil shortage and motor efficiencywith hydraulic diameter and area ratio. In the figure, the horizontalaxis represents the hydraulic diameter of each oil return passage, andthe vertical axis represents the area ratio (the ratio of the total areaof the oil return passages to an outer-diametral area of the statorcore, i.e., the area of a circle having a diameter equal to the outerdiameter of the stator core).

In a first region Z1, i.e., on condition that the hydraulic diameter is5 to 15 mm and the area ratio is 5 to 15%, then there is no problem inoil shortage or motor efficiency.

In a second region Z2, i.e., on condition that the hydraulic diameter islarger than 15 mm and that the area ratio is 5 to 15%, there is a slightproblem in motor efficiency, but no problem in oil shortage.

In a third region Z3, i.e., on condition that the hydraulic diameter is5 mm or larger and the area ratio is larger than 15%, there is noproblem in oil shortage but is a problem in motor efficiency.

In a fourth region Z4, i.e., on condition at least either that thehydraulic diameter is smaller than 5 mm or that the area ratio issmaller than 5%, there is no problem in motor efficiency but is aproblem in oil shortage.

Next, grounds of the graph of FIG. 5 are shown in FIGS. 6A, 6B, 7A and7B.

FIG. 6A shows a relationship between area ratio (ratio of the total areaof the oil return passages to the outer-diametral area of the statorcore) and motor-efficiency decreasing rate. In the figure, the verticalaxis represents motor-efficiency decreasing rate, where the motorefficiency decreases more and more downward of the vertical axis. As canbe seen from FIG. 6A, with the area ratio over 15%, the motor efficiencyis extremely decreases.

FIG. 6B shows a relationship between area ratio (ratio of the total areaof the oil return passages to the outer-diametral area of the statorcore) and oil-level decreasing rate. In the figure, the vertical axisrepresents oil-level decreasing rate, where the oil level decreases moreand more downward of the vertical axis. As can be seen from FIG. 6B,with the area ratio under 5%, the oil level extremely decreases.

In other words, since the motor efficiency decreases with increasingtotal area of the oil return passages, the area ratio (ratio of totalarea of oil return passages/outer-diametral area of stator core) needsto be smaller than 15%. Also, since a smaller total area of the oilreturn passages causes oil returnability to worsen, enough oil levelcannot be ensured. Therefore, the area ratio (ratio of total area of oilreturn passages/outer-diametral area of stator core) needs to be largerthan 5%.

FIG. 7A shows a relationship between hydraulic diameter of the oilreturn passages and motor-efficiency decreasing rate. In the figure, thevertical axis represents motor-efficiency decreasing rate, where themotor efficiency decreases more and more downward of the vertical axis.As can be seen from FIG. 7A, hydraulic diameters larger than 15 mm leadto occurrence of a problem in motor efficiency.

FIG. 7B shows a relationship between hydraulic diameter of the oilreturn passages and oil-level decreasing rate. In the figure, thevertical axis represents oil-level decreasing rate, where the oil leveldecreases more and more downward of the vertical axis. As can be seenfrom FIG. 7B, with the hydraulic diameter under 5 mm, the oil levelextremely decreases.

In other words, a larger hydraulic diameter causes the surface area ofthe annular portion 511 of the stator core 510 to become smaller, sothat the motor efficiency decreases. Therefore, the hydraulic diameterneeds to be smaller than 15 mm. Also, since a smaller hydraulic diametercauses oil returnability to worsen, enough oil level cannot be ensured.Therefore, the hydraulic diameter needs to be larger than 5 mm.

It is noted that the present invention is not limited to theabove-described embodiment. For example, the compression element 2 mayalso be a rotary type one in which its roller and blade are providedindependent of each other. The compression element 2 may further be ascroll type or reciprocating type one other than the rotary type. Thecompression element 2 may also be a two-cylinder type one having twocylinder chambers. The coils 520 may be of the so-called distributedwinding in which the coils 520 are wound over the plurality of teeth512.

Further, it is also allowable that the compression element 2 is providedabove while the motor 3 is provided below. The oil return passages 530may be provided on the inner circumferential side of the stator core510, or provided at an intermediate portion between the innercircumferential surface and the outer circumferential surface of thestator core 510. Furthermore, the oil return passages 530 may beprovided at any position in the circumferential direction of the statorcore 510, and may be provided at equal or unequal pitches.

1. A compressor comprising: a closed container having an oil reservoir;a compression element disposed within the closed container; and a motordisposed within the closed container, the motor being arranged to drivethe compression element via a shaft, the motor including a stator corehaving a plurality of oil return passages extending through a firstsurface of the stator core located on a side closer to the oil reservoirthan an opposite side and through a second surface of the stator corelocated on the opposite side, and a hydraulic diameter of each of theoil return passages at the second surface of the opposite side of thestator core being 5 mm or larger, and a ratio of a total area of theplurality of oil return passages at the second surface of the oppositeside of the stator core to an area of a virtual circle having a diameterequal to a maximum outer diameter of the stator core being 5 to 15%. 2.The compressor as claimed in claim 1, wherein the stator core isdisposed radially outside of a rotor of the motor, and the oil returnpassages are located on an outer circumferential side of the statorcore.
 3. The compressor as claimed in claim 1, wherein a refrigerant inthe closed container is carbon dioxide.